Investigators haven't determined what caused a Qantas Airbus A330 to pitch down uncommanded during an otherwise routine cruise in October 2008, but facts uncovered so far and revealed in an interim report out Wednesday (.pdf)
make a few things clear. One, the incident bares little resemblance to the crash of Air France Flight 447
beyond the basic facts. Two, the probe has helped convince Airbus to make software modifications that, according to the Australian Transport Safety Bureau (ATSB), be retrofitted throughout the entire fleet.Qantas Flight 72
was en route to Perth from Singapore on October 7, 2008 when, while cruising at 37,000 feet, the plane pitched down twice. A dozen on board suffered serious injuries, and the cabin was damaged. The plane diverted to Learmonth and landed safely.
Because of the accident's basic facts--an Airbus A330 cruising along apparently trouble-free suffers a malfunctioning air data inertial reference unit (ADIRU) and unexplained in-flight upset--it garnered much scrutiny following the still-unexplained June 1 loss of Air France Flight 447. But ATSB noted in its most recent report that there are several significant differences between the two accidents. From the ATSB report:
- The ADIRUs on the two aircraft were different models made by different manufacturers.
- The cockpit effect messages and fault messages from both flights showed a significantly different sequence and pattern of events. For example, a series of maintenance messages transmitted by AF447 prior to the accident showed inconsistencies between the measured airspeeds as well as the associated consequences on other aircraft systems. No such messages were recorded by VH-QPA on 7 October 2008.
- The airspeed sensors (pitot probes) on the two aircraft were different models made by different manufacturers. (The Qantas aircraft has Goodrich-made probes, not the Thales probes that are the subject of airworthiness directives requiring replacement with the Goodrich models.)
Meanwhile, Airbus has determined that changes to A330/A340 flight control primary computer (FCPC or PRIM) software is necessary. Quoting ATSB:
Airbus is modifying the flight control primary computer (FCPC or PRIM) software used in the A330/A340 fleets to prevent any future similar problems leading to an uncommanded pitch-down event. An interim modification to the FCPC software standard is being installed in the operator's fleet, and the installation is expected to be completed by the end of November 2009. A later FCPC software standard to improve the treatment of all ADIRU parameters will be certified in mid to late 2010, and will then be retrofitted to the world-wide fleet of A330/A340 aircraft.
So, what caused Qantas Flight 72 to dive twice without pilot input? Investigators are investigating away. Turbulence or other meterological factors have been ruled unlikely contributors. Detailed tests of the ADIRUs have turned up nothing out of the ordinary. Cosmic/solar radiation interference is being considered. Bottom line: "the investigation is still following several lines of inquiry to explain why the ADIRU started providing erroneous data," ATSB said.